A program, covering the principal factors affecting man's physiological and behavioral response to his thermal environment and their implications for his health, consists of six projects: 1. Characterization of Man's Thermal Environment: rational environmental indices of environmental stress and strain will be developed based on direct measurement of heat and mass transfer characteristics of the thermal environment. 2. Physiological Responses to Warmth and Humidity: A standardized test for thermoregulatory efficiency will be developed based on studies of temperature regulation in warmth and response to acclimation by exercise and heat. 3. Physiological Responses to the Cold: Control of shivering metabolism, cold acclimation and corresponding role of age, sex, length of exposure, and physical condition will be studied with emphasis on moderate cold. 4. Physiological Bases of Discomfort and Thermal Acceptability: Physiological bases of thermal discomfort and enviromental acceptability will be related to acclimation, age, sex and ill health. 5. Psychophysics of Thermal Sensation and Human Performance: Sensory and behavioral responses of man to his thermal environment will be studied with emphasis on cold. 6. Epidemiology of The Thermal Environment: Association between outdoor ambient temperature and humidity and mortality and morbidity will be studied with special emphasis on role of the indoor environment and its physiological stress.